The present invention relates to superconducting structures and to a method of improving superconducting flux pinning properties of selected mixed (RE1/RE2) Ba2Cu3O7 films, where RE1 and RE2 are selected rare earth elements. This invention was made with government support under Contract No. W-7405-ENG-36 awarded by the U.S. Department of Energy. The government has certain rights in the invention.
Since the discovery of high-temperature superconducting (HTS) materials (superconducting above the liquid nitrogen temperature of 77 K) there have been efforts to research and develop various technology and engineering applications using such HTS materials. In thin film superconductor devices, the most progress has been made with fabrication of devices utilizing an oxide superconductor including yttrium, barium, copper and oxide in the well-known basic composition of YBa2Cu3O7xe2x88x92x (hereinafter referred to as Y123). At liquid nitrogen temperatures and in high magnetic fields, the. Jc of Y123 is superior to those of the bismuth, thallium and mercury based HTS materials. Thus, Y123 has been the preferred material for many applications.
Even though Y123 is the material of choice for HTS applications, it has drawbacks. One drawback is that Y123 has one of the lowest Tc""s among (RE)Ba2Cu3O7xe2x88x92x materials (hereinafter referred to as (RE)123) which can limit Jc at the liquid nitrogen temperature (since Jc depends on Tc; Jc≈(1xe2x88x92T/Tc)3/2). Still another drawback is that other RE123 materials such as Nd123 have a larger Jc in high magnetic fields than Y123. Hence, it has been important to continue development of (RE)123 films for various HTS applications.
There have also been several efforts at combining mixed rare earth elements in bulk materials to improve flux pinning. For example, Matthews et al., Physica C, vol. 249, pp. 255-261 (1995) describe increased Jc for bulk samples of(Nd1xe2x88x92yYy)123 in magnetic fields comparison to Y123 samples. Schaetzle et al., Supercond. Sci. Technol., vol. 9, pp. 869-874 (1996) describe the preparation of bulk samples of (Sm1xe2x88x92yYy)123 and (Nd1xe2x88x92yYy)123. Schaekle et al. show higher Jc""s for (Nd1xe2x88x92yYy)123 than Y123 in a magnetic field, but show that (Sm1xe2x88x92yYy)123 has lower Jc""s than Y123 in a magnetic field. Saitoh et al., Physica C, vol. 288, pp. 141-147 (1997) describe Jc""s in a magnetic field for (RE,RExe2x80x2)123""s where RE and RExe2x80x2 are rare earth elements from the group of yttrium, neodymium, europium, gadolinium and sarmarium.
Despite the variety of work with bulk materials, there have been no know attempts at forming thin films of mixed rare earth element containing 123 compositions. Thus, an object of the present invention is thin film compositions of various (RE1/RE2)123 films.
Another object of the present invention is a process of forming various (RE1/RE2)123 thin films with enhanced flux pinning properties by forming multilayer compositions with alternating layers of (RE1)123 and (RE2)123 films.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a superconductive structure including a substrate and a thin layer of a superconducting rare earth-barium-copper.oxide ((RE)123) film thereon, the thin layer including at least two rare earth elements (RE1 and RE2).
The present invention also provides a method of improving the superconducting flux pinning properties of a superconducting (rare-earth)-barium-copper oxide structure by forming alternating thin film layers including at least a first thin layer of a first rare earth-barium-copper oxide ((RE1)123) film directly on a substrate and forming a second thin layer of a second rare earth-barium-copper oxide ((RE2)123) film.